This invention relates generally to systems for measuring electrical energy consumption from a transmission system, and more particularly to an electronic system for measuring electrical energy consumption from a three-phase transmission system.
A commercially available electronic watt-hour meter which is used for measuring the consumption of electrical energy from a single phase alternating current transmission system is described in German Patent DE-OS No. 27 47 385. The system described therein receives an electrical signal which corresponds to the load current of the system for controlling a duty cycle modulator. The output signal of the duty cycle modulator is applied through logic circuitry to an analog control switch which controls the conduction of a second input signal which corresponds to the load voltage. The analog switch, however, is shunted by complex amplification circuitry so as to produce a signal which corresponds to a preselected fraction of the second input signal. This signal, corresponding to the preselected fraction of the load voltage input signal, is conducted to a current-to-frequency converter which consequently controls a counting device. The count stored in the counting device, therefore, corresponds to the energy consumption of the load.
In order to apply the energy measuring system of German Patent reference DE-OS No. 2747 385 to multiphase systems, the system described hereinabove with respect to a single phase transmission system must be replicated for each phase of interest. Such replication, however, is complex and expensive because each analog switch must be shunted by the amplification circuitry.
In view of the foregoing, it is an object of this invention to produce a multiphase watt-hour meter which is simpler, less costly and requires less space than the replication of a single phase system.